Isoelectric Focusing Using Electrokinetically-generated Pressure Mobilization

Porous polymer monoliths (PPM) are an increasingly important and popular class of materials finding applications in fields such as separation, purification, cell and tissue culturing, storage of liquids and gases, energy storage, structural applications, supports for catalysts and reagents, etc. In contrast to particulate polymer material, monoliths are defined as intractable articles with a homogeneous microstructure. While the method of preparation and the chemical composition largely govern the resulting porous structure, the porous monoliths can be characterized by their pore size profile (micro‐, meso‐, macroporous material), morphology (interconnected or isolated pores, shape of pores), total porosity (pore volume), surface area, and special features, for example, hierarchical porous structure. Meso‐ and micropores mainly contribute to the total surface area of the monolith, whereas macropores, if interconnected, enable the convective mass transfer through the monolith and reduce the overall density of the material. Obtaining PPM with a multimodal pore size distribution is possible via a combination of methods or by a postpolymerization treatment. This is a useful feature allowing the production of materials with tailored porous structure for specific applications where macro‐ and micropores are needed. Generally, the methods for PPM preparation can be divided between templating (two phases are present during the preparation, of which one templates the porosity) and nontemplating (one phase system, eg, phase separation induces pores). This paper introduces the various methods and focuses on the emulsion templating approach. Recently introduced chemistries and combinations of methods as well as new examples of applications are highlighted.

Preparation of stable water-in-oil (W/O) high internal phase emulsion (HIPE) containing methyl methacrylate (MMA) monomer as oil phase is a difficult task due to the significant solubility of MMA in water. Here, for the first time a fluorinated di-block copolymer (FDBC) poly (2-dimethylamino)ethylmethacrylate-b-poly (trifluoroethyl methacrylate) (PDMAEMA-b-PTFEMA) is proposed to stabilize HIPEs of MMA without the use of any co-stabilizer or thickening agent. Fluorinated segments in FDBC anchored well at oil/water interface of HIPE, offering high hydrophobicity to the partially hydrophilic MMA monomer and in turn stabilization to MMA-HIPE. By using fluorinated di-block copolymer as stabilizer, highly stable HIPEs can be obtained. In addition, highly interconnected porous monoliths were obtained after free radical polymerization, which are highly desirable materials in various practical applications including tissue engineering scaffolds, separation science, bio-engineering and so on. The as-prepared MMA-HIPEs possess high thermal stability without phase separation. The textural characteristics of as-prepared composites, such as pore size and distribution, can be easily controlled by simply varying the amount of FDBC and/or dispersed phase fraction. Moreover, the influence of di-block concentration on water uptake (WU) capability of the prepared porous monoliths is explored.

Fabrication of interfacial functionalized porous polymer monolith and its adsorption properties of copper ions

The effect of pre‐modification on the interaction of macroporous substrates (membranes) with mainly micro‐ and mesoporous polymer monoliths has been studied. Bulk, porous polymer monoliths were synthesized to optimize the synthesis conditions and their pore morphology, and the data were used as benchmark for this study. Pre‐modification of the entire pore surface of PP microfiltration membranes and PET track‐etched membranes by UV‐initiated grafting with PEGMA was performed using well‐established methods, including coating with the photo‐initiator, benzophenone. Subsequently, these membranes were functionalized by filling the pores with porous polymer monoliths from MAA and EDMA and compared with membranes that had been functionalized without the pre‐modification step. The materials were characterized mainly by the degree of grafting, SEM and by the gas‐adsorption‐isotherm method. The DG values, after composite‐membrane preparation under identical conditions, were not influenced by the pre‐modification. However, it could be clearly seen from the SEM images that the pre‐modification step prevents the formation of voids at the monolith‐membrane pore interface. Larger specific surface area and pore volume values for composite membranes, prepared after pre‐modification, fully support the SEM results. Especially large differences in pore structure between the two different composite membranes were found in the mesopore range. The results of this study indicate that it is possible to prepare porous, composite membranes where the trans‐membrane transport is exclusively controlled by the pore and surface structure of a functional polymeric monolith, for example, made from a molecularly‐imprinted polymer.magnified image

The development of organic porous polymer monoliths represents an alternative approach to stationary phase design. The use of these materials has helped to rekindle interest in capillary electrochromatography. Although a large number of investigations have explored different monolith recipes, polymerization conditions, and application challenges, few investigations have addressed the fundamentals of this separation mode with this type of material. This study addresses the thermodynamics of the reversed phase retention mechanism on 100% butyl acrylate and 1:3 butyl:lauryl acrylate (volume/volume ratio) porous polymer monoliths used in a capillary electrochromatography mode. Linear van't Hoff plots yield enthalpies of retention of -3.9 to -14.3kJ/mol on two different, but related columns for five selected hydrophobic analytes across a thirty degree temperature range. Minimum plate heights were only moderately impacted over this temperature range.

Porous monoliths prepared by high internal phase emulsion (HIPE) templating have received various attentions in the fields of catalysis, separation, and tissue engineering. However, the application of the monoliths from HIPE is limited by their poor mechanical performance and the difficulty of fabricating hierarchically porous structures. Additive manufacturing is an emerging technique that achieves high design freedom by depositing materials layer‐by‐layer. This work designs medium internal phase emulsion (MIPE) ink with the concept of miniemulsion to prepare 3D printable porous polymeric monoliths with sub‐micrometer pores. High shear energy is used to reduce the droplet size of the internal phase and jam the emulsion ink. The jammed MIPE ink shows prominent shear‐thinning behavior and appropriate elastic modulus for direct ink writing (DIW). After printing, the external phase composed of stearyl acrylate and hexanediol diacrylate can be cured by photopolymerization to produce poly(MIPE) with interconnected pores in the size of several hundred nanometers. The printed poly(MIPE) demonstrates high mechanical strength and can be reprogrammed into complex geometries difficult for the common DIW processes. The proposed technique provides a new route to fabricate hierarchically porous monoliths with a drastic change of pore dimension, high mechanical strength, and tunable shape reconfiguration.

Surface-mediated effects on porous polymer monolith formation within capillaries

Nucleic acid sandwich assays improve low-density array analysis through theaddition of a capture probe and a specific label, increasing specificity andsensitivity. Here, we employ photo-initiated porous polymer monolith (PPM) as ahigh-surface area substrate for sandwich assay analysis. PPMs are shown toenhance extraction efficiency by 20-fold from 2 μl ofsample. We further compare the performance of labeled linear probes, quantum dotlabeled probes, molecular beacons (MBs) and tentacle probes (TPs). Each probetechnology was compared and contrasted with traditional hybridization methodsusing labeled sample. All probes demonstrated similar sensitivity and greaterspecificity than traditional hybridization techniques. MBs and TPs were able tobypass a wash step due to their ‘on–off’signaling mechanism. TPs demonstrated reaction kinetics 37.6 times faster thanMBs, resulting in the fastest assay time of 5 min. Our data further indicate TPshad the most sensitive detection limit (<1 nM) as wellas the highest specificity (>1× 104 improvement) among all tested probesin these experiments. By matching the enhanced extraction efficiencies of PPMwith the selectivity of TPs, we have created a format for improved sandwichassays.

Cross‐linked monolithic polymer networks (or dried gels) with hierarchically porous structures have been prepared by controlled/living radical polymerization techniques such as nitroxide‐mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), and organotellurium‐mediated living radical polymerization (TERP). Well‐controllable macropores are formed as a transient structure of spinodal decomposition induced during the polymerization of monomers, and smaller pores in the macropore skeletons are resulted from secondary phase separation during the phase separation–gelation process. Also, the obtained networks are pyrolyzed in an inert atmosphere to obtain carbonaceous materials with abundant micropores while preserving the macro‐ and mesoporous morphology. In addition, applications of such hierarchically porous monolithic materials to separation media and electrochemical devices are demonstrated. In the present article, the concept, mechanism, methodology, and experimental results are discussed in detail.

Molecular interactions between wall polysaccharides, which include cellulose and a range of noncellulosic polysaccharides such as xyloglucans and (1,3;1,4)-beta-D-glucans, are fundamental to cell wall properties. These interactions have been assumed to be noncovalent in nature in most cases. Here we show that a highly purified barley xyloglucan xyloglucosyl transferase HvXET5 (EC 2.4.1.207), a member of the GH16 group of glycoside hydrolases, catalyzes the in vitro formation of covalent linkages between xyloglucans and cellulosic substrates and between xyloglucans and (1,3;1,4)-beta-D-glucans. The rate of covalent bond formation catalyzed by HvXET5 with hydroxyethylcellulose (HEC) is comparable with that on tamarind xyloglucan, whereas that with (1,3; 1,4)-beta-D-glucan is significant but slower. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analyses showed that oligosaccharides released from the fluorescent HEC:xyloglucan conjugate by a specific (1,4)-beta-D-glucan endohydrolase consisted of xyloglucan substrate with one, two, or three glucosyl residues attached. Ancillary peaks contained hydroxyethyl substituents (m/z 45) and confirmed that the parent material consisted of HEC covalently linked with xyloglucan. Similarly, partial hydrolysis of the (1,3;1,4)-beta-D-glucan:xyloglucan conjugate by a specific (1,3;1,4)-beta-D-glucan endohydrolase revealed the presence of a series of fluorescent oligosaccharides that consisted of the fluorescent xyloglucan acceptor substrate linked covalently with 2-6 glucosyl residues. These findings raise the possibility that xyloglucan endo-transglucosylases could link different polysaccharides in vivo and hence influence cell wall strength, flexibility, and porosity.

On-chip solid phase extraction and enzyme digestion using cationic PolyE-323 coatings and porous polymer monoliths coupled to electrospray mass spectrometry

Polymerized high internal phase emulsions (poly(HIPE)s) are porous polymer monoliths whose synthesis can easily be tailored to allow incorporation of functional units. In this work, nitrile containing poly(HIPE)s have been prepared with either acrylonitrile (AN) or 4-cyanostyrene (4CS) comonomers. Post-synthetic modification of these nitrile-containing poly(HIPE)s yields their corresponding amidoximated analogues, which were studied for actinide uptake. These amidoxime-functionalized, porous polymers were shown to adsorb 95 % Th4+ species from aqueous solution within 30 minutes. In contrast to other amidoxime containing polymers the uptake of UO2 2+ in these poly(HIPE)s is lower under similar conditions. A critical analysis of actinide separations and high-energy X-ray scattering data provides insight into the polymers' selectivity, enabled by the uptake of multinuclear Th clusters.

Impact of mobile phase composition on the performance of porous polymeric monoliths in the elution of small molecules

Capillary Electrochromatography: A Rapidly Emerging Separation Method.- Short Monolithic Columns as Stationary Phases for Biochromatography.- Porous Polymer Monoliths: An Alternative to Classical Beads.- Molecularly Imprinted Materials - Receptors More Durable than Nature Can Provide.- Chromatographic Reactors Based on Biological Activity.- Simulated Moving Bed Chromatography (SMB) for Application in Bioseparation.- Continuous Annular Chromatography.

Tests were made on highly purified bovine peptidal pituitary factors for lipolytic activity on rat adipose tissue. The lipolytic protein factor from bovine pituitary glands was isolated and characterized by ethanol precipitation, gel filtration, and isoelectric focusing. The supernatant of the homogenized tissue was precipitated with ethanol, the precipitate was lyophilized and resuspended in HCl 1 mmole/liter, the insoluble was discarded, and the supernatant lyophilized. A solution of the lyophilized fraction was fractionated by gel filtration on Sephadex G-75. The bands with lipolytic activity were pooled and lyophilized. Lipolytic activity was determined by incubation of epididimal rat adipose tissue and by successive measurements of free fatty acids and glycerol released in the incubation medium. The gel filtration with the highest lipolytic activity (20.4 µequiv/g per 4 hr and 17.0 µmole/g per 4 hr glycerol) was submitted to isoelectric focusing. The gel filtration still appeared highly heterogeneous, but most of the lipolytic activity was concentrated in the protein band at pH 8.6.